Microwave Drive

[kach22i]

Theory started as an engine for spacecraft. Could this be made to work under water?

http://www.ghacks.net/2007/08/02/off...oming-reality/

prototype of a propeller that uses microwaves to generate thrust and by doing so compensate the power of gravity…

[kach22i]

Maybe this old thread idea was not so crazy?
Surface Piercing Foil Damping

[mydauphin]

May be Bugatti Yachts will advertise it to their many customers....

[marshmat]

I've seen that thing before.... it looks plausible. Better to read the physicists' own paper on it, http://emdrive.com/theorypaper9-4.pdf which is somewhat more honest with the numbers than the media hype can be (if, that is, you're OK with the math behind waveguides and special relativity). Especially worth noting is that the specific thrust is said to be on the order of 333 millinewtons per kilowatt at 3 km/s- for our friends who prefer the old units, think about one ounce of thrust per horsepower. (Problem- I can't figure out what that 3 km/s velocity is relative to; the waveguide should only care about the craft's own reference frame, right?)

For a spacecraft, that's enormous- the ion engine on NASA's DS1 probe was only good for 92 millinewtons, and it had to carry something like 74 kg of xenon propellant to get two years of thrust. Still, that works out to a specific impulse ten times better than conventional chemical propellants. If this waveguide thing works, we could have much greater thrust, for as long as the sun shines on the solar panels.

But I wouldn't count on seeing it on a boat or airplane anytime soon.